Application of b- and z- values statistics upon the precursor study, cases of the larger earthquake of Taiwan

• Main Authors: Chiao-Chun Yao, 姚喬鈞
• Other Authors: Tsui-Yu Chang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/48234784136340736468

碩士 === 國立臺灣海洋大學 === 應用地球科學研究所 === 94 === Abstract We took advantage of the seismic catalog compiled by the Central Weather Bureau for studying the possible seismicity precursor before the large earthquakes for the Taiwan area. Seismic data adopted from 1990 to 2005, with the criteria of seismic magnitude larger than 5.0 and focal depth less than 40 km, were applied to conclude the relationship between the precursory period prior to the occurrence of large crustal earthquake. The seismicity sampling spaces were defined with the radii of 20 and 50 kilometers, respectively to estimate the near-field and large field seismicity change. The other search the area where high earthquake probability near main earthquake for the calculation of z value. Along the seismic time sequence, the sudden drop of b and z values were considered as the index of moment reflecting seismicity change corresponding to the coming large event. The duration between this moment and the main shock was defined as the possible precursory time (denoted as △t) for the large earthquake. We compared each precursory time with the magnitude, focal mechanisms and spatial and temporal distributions of these main. In general, △t was larger at the eastern part than the western Taiwan. △t obtained form z value were increasing with time from 0.22 to 0.32 years. However, △t focused within the range of 0.12 to 0.15 years for the larger earthquakes. The comparison with the varied focal mechanisms showed that △t seemed nothing with the different rupture process. It's observed that the seismic frequency was obvious increasing for the period just prior to the large earthquake. Our study illustrated that the b and z statistics can detect such an increasing of seismicity rate. The duration between the moment of obvious variation of the two values and main earthquake is within the range of 0.12 to 0.2 years. The standard deviation of △t obtained form high earthquake probability less then obtained form the radii of 20 and 50 kilometers.